While RBL cells are common system for studying secretion, existing data seems to indicate that the plasma membrane area does not change, contrary to the results in a number of other secretory cells. However, the data are based on whole cell capacitance measurements (under conditions in which RBL cells have been found not to secrete), and on serial electron microscopy reconstruction of cells (which is a less accurate technique than capacitance measurements). We propose to do permeabilized patch capacitance recording of RBL cells, thus allowing electrical access to the whole cell membrane while maintaining the cytoplasmic integrity necessary to have secretion.